In this paper, a method for Reactive Power Planning (RPP) is proposed which ensures voltage stability in a system with cross-border electricity flows. One or more cross-border tie-lines connect the Source-area, containing cheap generation, to the Sink-area which is willing to import this cheap power. A mathematical method is used to maximize the economic benefit of the Sink-area with respect to the cost of the installed reactive compensators which maximize the Net Transfer Capacity (NTC) of the tie-lines. An analytic expression for the NTC does not exist and two methods are henceforth proposed to approximate the NTC: (1) approximation by a piecewise linear function and (2) by a polynomial obtained with statistical regression. The method is programmed in GAMS and formulated as a Mixed-Integer Non-Linear Programming problem (MINLP).

In order to have a reliable and secure power system, frequency stability should be guaranteed. Primary Frequency Response (PFR) is used to arrest the frequency deviation upon a contingency. The significant penetration of wind generation in power grids has negative effect on the PFR, as the contribution of wind machines to the total system inertia is low and classical wind turbines do not have PFR capabilities. This study uses two metrics of frequency control, ROCOF and frequency Nadir to analyze the cost increase for maintaining adequacy in the presence of wind power. The Nordic 32-A test grid, representing the Swedish grid is used as case study on which the method is applied.

The significant penetration of wind generation in power grids has raised new challenges in operational and planning decisions of power systems. Wind turbine units almost always include power converters decoupling the frequency dynamics of the wind power generators from that of the grid. This decoupling causes a reduction in total system inertia, affecting the system's ability to overcome frequency disturbances [1]. To study the impact of wind power on system inertia, a system identification approach is followed. This heuristic identification method determines the parameters of governors and prime movers. The instantaneous minimum frequency requirements and the rate of change of frequency are simulated using the identified power system, and via an extrapolation, the maximum wind power penetration in Sweden is found. Finally, a need for market design is introduced in order to ensure adequacy.